The mode of action of the Kensey catheter, a new atheroablation device, was investigated. Fresh above-the-knee amputated leg were used for recanalization of the superficial femoral artery. The variables used were identical to those of clinical trials, including a rotational speed of 50,000 rpm and an injection rate of 40 mL/min. The debris produced by the catheter was studied cytologically, and the arterial segments were examined histologically. The particle size in the debris ranged from 1 to 2,000 μm. The softer plaques produced a fine fibrin dust background with long strips of intima ranging from 10 to 2,000 μm. Complicated calcified plaques produced larger background material (10-120 μm) but smaller strips of intima (50-800 μm). Dissections and perforations occurred. Some of the debris produced by the atheroablation process was used to embolize a canine heart and kidney. Small focal infarctions were found in the heart, and large and multiple infarcts were seen in the kidney. In clinical studies the debris appears to be tolerated in the lower extremities. Its safety in the kidney and heart are questioned.